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Got a technical problem? Can't understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097; or send us an email.

IR touch dimmer zapped by fluorescents

I've recently assembled the Touch Dimmer project from the January & February 2002 issues. It operates well but its behaviour is affected by the switching off of any fluorescent light in the house. Whenever a fluorescent light is switched off, it will switch off the light that's controlled by the dimmer or change to an oscillating mode where the light fluctuates between different levels of brightness.

Can you suggest a remedy.

(A. C., via email).

The problem is probably caused by interference from the fluorescent lights. The interference could be either conducted along the power lines or radiated directly from the fluorescent light to the infrared sensor in the touch light dimmer control.

To check where the problem lies, cover the infrared sensor dimmer with an opaque material so it cannot respond to light. If the dimmer is now not affected, then some shielding of the dimmer from the fluorescent lights may be necessary. Repositioning the dimmer in a darker or protected position may be required.

Alternatively, remove the infrared sensor (IC2) from the touch lamp dimmer and connect pin 9 of IC1 to pin 5. Check if the fluorescent lights now have an effect. If so, you may require better shielding, particularly from the house wiring. An earthed metal shield behind the dimmer unit may be sufficient to protect it. A .01μF 250VAC (Y class) capacitor connected between the Active and Neutral lines may also help with reducing interference.

Thirdly, the fluorescent lights themselves may need a power factor correction capacitor in each fitting. Have these installed by your electrician. The capacitor will act as a power line filter as well as correcting power factor.

You may also need to replace the starters in each fluorescent fitting as the suppression capacitor in these may have failed, particularly if the starters are old.

Dry cell rejuvenator

Will the dry-cell Battery Rejuvenator from the November 1994 of SILICON CHIP successfully charge "D" size cells?

(J. C., Murray Bridge, SA).

The circuit should work with D cells although charge time will be a lot longer. It takes around 18 hours to recharge an alkaline AA cell.

Substitute display for the MP3 jukebox

The MP3 Jukebox works great except that the display is very hard to see from five metres away. Would I be able to use the Moving Message Display (SILICON CHIP, February 1997) as a substitute for the MP3 Jukebox display? If so, what modifications will I need to do in order for this display to work with the MP3 JukeBox?

(T. W., Girraween, NSW).

Unfortunately, the Moving Message Display from the February 1997 issue is not compatible with the MP3 Jukebox. Both the hardware and firmware on the IR Remote PC board is designed to work with LCDs that are "HD44780" compatible, with 16 x 2 format. This limits the possibilities somewhat, unless you modify the microcontroller program.

You could try a "large character" LCD (with LED backlighting). Farnell stock a suitable item: Varitronix MDLS16268-C-LED04 (order code 301-3340). See:

This module has 4.84 x 9.22mm characters, which are almost twice as big as the standard modules. Note that you should keep the cable between the PC board and the LCD module as short as possible - no more than about 150mm, if possible.

Video monitor degaussing

One of the kids put a magnet to the computer screen and it has a green tinge. Can it be fixed?

(B. M., via email).

The shadow mask in your monitor has evidently become heavily magnetised, so much so that the normal inbuilt degaussing coil may not be capable of fully curing it. You could try turning it on and off several times, leaving at least five minutes between. If that doesn't work you will need to take it to your local serviceman to be degaussed.

Battery load tester

Has there been a project or article written regarding load testing a car battery or other heavy duty batteries? I have need for a device for testing the condition of heavy duty batteries. Even if a project may not be viable, the methodology for load testing a battery, statistics and figures may be an interesting topic for some.

I was prompted for such a device after my car battery of 18 months began to intermittently fail to crank the engine. The NRMA technician, who attended after I eventually determined the battery to be at fault, confirmed my view of a defective battery with a load testing device. I also have a need for a device in the rail preservation scene, with many batteries of unknown quality needing a basic Go/No-go test to determine their future.

(R. P., Cowra, NSW).

Car battery load testing is usually done with a "carbon pile". Auto-electricians have them. Generally though, you can do a rough and ready test by just turning on all lights; ie, low beam + high beam. A marked drop at the battery terminals indicates a real problem. Testing large storage batteries is more problematic and needs to be done at specified load conditions for the particular battery.

Crossfire problem in multi-spark ignition

I built myself a Multi-Spark Ignition System, (SILICON CHIP, September 1997). It went into a 1977 Fairlane V8 and I used the Hall Effect pickup. The car runs well on idling but as soon as I try to accelerate, the ignition breaks down; the engine sounds as if it is running on two cylinders.

I looked for crossfire but did not notice any. I would appreciate it very much if you could tell me what the problem might be.

(U. S., via email).

Since the engine is a V8, there is always a strong likelihood of crossfire, particularly when the engine is under load.

Try reducing the number of multi sparks with the capacitor, as detailed in the article. If this does not help, change the operation to single spark. If it is still misfires, it probably does have crossfiring and all the ignition leads will need to be separated widely to prevent this.

Higher speed setting for PC infrared transceiver

Having recently built the PC Infrared Transceiver from the December 2001 issue, I was wondering what is involved in taking the unit's speed from SIR (115.2kbps), the default setting, to the next higher speed of MIR (1.152Mbps)?

Is it a matter of changing external components or is it permanently set by the TFDS4500 transceiver module internals?

I realise that this speed was chosen to support all types of Pentium motherboard and the unit works well, but a change in speed would be very welcome as I have a motherboard that supports the higher IR transmission rates.

(B. C., via email).

Unfortunately, the maximum rate is determined by the TFDS4500 module, which you correctly state at 115.2kbps.

We may publish something faster in the future (MIR and/or FIR) but we can't give any guarantees. If you're keen to upgrade soon, you might consider a commercial solution.

Microgram Computers often advertise IR add-ons - check them out at

Ammeter has stopped working

I recently constructed the 80A Automotive Ammeter from the June 2002 issue and it was working well. However, it now fails to give any correct indication of current levels.

When I attempted to re-calibrate the unit at the 'zero' current level, the 'CAL' LEDs light but on removal of the shorting plug, the indication goes to 'OL'. Attempts to calibrate at other levels bring either totally erroneous (high) readings or the 'OL' indication again.

The ammeter is an important part of my domestic solar system. I gather it should work satisfactorily in this situation?

(R. T., Darbys Falls, NSW).

Perhaps there is a short in the Hall effect wiring or the Hall sensor is not working. Check that the Hall effect unit is receiving its 5V supply and that its output is around 2.5V.

Alternatively, there may be a problem with the LM358 and associated components. Check its supply and that the output is a varying voltage, indicating that the conversion process is working.

Operating the turbo timer from 24V

Is it possible to operate the turbo timer (SILICON CHIP, November 1998) on 24V DC. If so, what mods do I need to make?

(G. S., via email).

It is possible to operate the turbo timer from 24V. Change the 33Ω resistor to ZD1 to a 680Ω 1 W resistor and change ZD1 to a 15V 1 W zener. Also, change the 10kΩ resistor connecting between ground and the 1.8kΩ resistor to 1kΩ.

Also the relays will need a series resistor with the 12V relay coil to limit the voltage across their coils. Measure the coil resistance in ohms and use a 5W resistor of the same value in series with the coils.

Low fuel warning indicator

Is it possible to modify the Low Fuel Warning Indicator kit (SILICON CHIP, February 1993) so that it can be used as a warning light for low oil pressure instead?

The circuit works in conjunction with the fuel sender in the tank and you set the parameters relative to where the gauge is registering, so I was wondering if it was possible to remove the components that create the 10-second delay and use it as a low oil pressure warning light instead. Also would it be versatile enough so that you can select a relatively high oil pressure, say around 20-30 psi? I wouldn't care if it glowed at idle when the oil was hot.

I ask this because cars that come with inbuilt gauges on the dash as standard never have an indicator light as well.

(B. S., via email).

The low fuel indicator can be used for other measurements. The 10kΩ resistor in series with VR1 can be reduced in value if the range is not sufficient. The delay may be reduced but it may still be necessary to have a small delay to prevent false triggering. Use a 10μF capacitor instead of the original 220μF delay capacitor.

IR transceiver is possibly damaged

I bought the kit to make the IR transceiver published in the December 2001 issue. I tried it out on my Win2000 and it didn't detect it automatically, so I tried to configure it manually and it still didn't work. The circuit has been checked out OK and I would like to know what needs to be done now to get it working.

I have enabled IR in BIOS and it is set as IrDa and the Tx Rx stuff is Hi Lo respectively. I don't know if that makes any sense. From your documentation and the stuff I have seen on websites, it should be detected automatically.

I downloaded something from Microsoft called IRCOMM, as it was a patch 2000 apparently needed. Currently, I have Service Pack 2 installed and some pre-Service Pack 3 fixes. Your help would be greatly appreciated.

(A. M., via email).

You should be able to verify that the IR LED inside the TFDS4500 module is not damaged by using your DMM. Switch your DMM to "Diode Test" and measure between pins 1 & 8 of the TFDS4500. With the positive DMM probe on pin 8 and negative probe on pin 1, you should get a reading of about 1.23V. Reverse the leads and you should get no reading (high resistance).

You should refer to the "Mailbag" pages in the May 2002 issue for additional information about motherboard BIOS settings. Microsoft provide the following general info about irDA setup on Win 2000: How To Configure Your Computer for Infrared Communication in Windows 2000 (Q302011). See:;en-us;Q302011


SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws.

Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable.


Whistle & Point Cable Tracer, October 2002: the pinout diagram for the C8050 package (circuit, page 54) is incorrect. The C8050 collector & emitter pins are reversed with respect to common general-purpose TO-92 transistors like the BC549.

5A Speed Control, October 2002: the 100nF capacitor shown on the PC board diagram on page 17 should be 47nF to agree with the circuit on the same page.

Note also that the pinout diagram for the MCR100 on the circuit is wrong with regard to the Anode and Gate pins. The gate is the centre pin of the package as it is with the C103B however the A and K pins are swapped.

40W Fluorescent Inverter, September 2002: due to tolerance variations within the L6574 (IC3), it is recommended that the maximum current delivered to the fluorescent tube be adjusted using a trimpot. The 100kΩ resistor connecting between pin 2 of IC3 and the top of the dimming potentiometer (VR1) should be replaced with a 50kΩ trimpot and series 82kΩ resistor. The 1.2Ω resistor between the source of Q4 and ground should be changed to 2.2Ω to allow the full dimming range available from VR1.

Using the current measuring setup of Fig.8, the trimpot should be adjusted for the 370mV, corresponding to 3.7A when the dimming pot (VR1) is turned fully clockwise. Note that this adjustment should be made after the inverter has been running for some time and is fully warmed up. Once adjusted, the trimpot and 82kΩ resistor can be swapped for a single resistor that is the same value as the total series combination.

When testing the current (using the setup of Fig.8), it is important not to have the 0.1Ω 5W resistor in series with the supply for any appreciable length of time as the current drawn will begin to increase. To prevent this, short out the 0.1Ω resistor (with a clip lead) when not making the measurement. Remove the clip lead briefly to make the current measurement.

In addition, use heavy gauge wire rated at 7.5A or more to connect the inverter to the 12V battery.

The lower cost MTP3055E Mosfets can be substituted for the STP60NE06 devices used for Q1 and Q2.

The Dick Smith Electronics D-5375 ferrite core is also suitable for L2 and requires 100 turns of wire (50 turns on each half) instead of the 84 total shown in Fig.6.

4-Channel UHF Remote Control, July 2002: the circuit diagram on page 20 is incorrect. On the PC board overlay diagram, the collectors of all four transistors (Q1-Q4) connect first to 2.2kΩ resistors, then to their respective LEDs. However, the resistors and LEDs are swapped on the circuit diagram.

MP3 Jukebox, September/October 2001: since publication of this project, version 2 of the Winamp software has been superseded by version 3. Unfortunately, Winamp version 3 is not suitable for use with the MP3 Jukebox. However, the last release of version 2 (v2.8.1) can be downloaded from

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